In optical communication systems, for a variety of the signal processing, various optical waveguide devices are used. Such optical waveguide devices are represented by, e.g., optical branch/coupling devices, for branching into optical signals by arbitrary ratios, etc. As an optical branch/coupling device for obtaining an arbitrary optical branching ratio is known an optical waveguide device including two 2:2 optical couplers and an optical phase shifter provided between the optical couplers and having two waveguides for giving a phase difference.
As techniques for giving a phase difference to two optical waveguides of the optical phase shifter are proposed, e.g., the technique of providing linear waveguide regions of a relatively small width to control the lengths of the regions, the technique of forming two waveguides in tapered waveguides of different taper angles, the technique of providing in one waveguide a delay interferometer formed of a bent optical waveguide, and other techniques.
The followings are examples of related: Japanese Laid-open Patent Publication No. 2004-144963; Japanese Laid-open Patent Publication No. 2005-249973; and Japanese Laid-open Patent Publication No. 2006-293345.
However, the countermeasures against the manufacturing tolerance are not considered enough in the above-described techniques. Thus, the phase change amounts are often greatly shifted by the variations in manufacturing the waveguides, etc. from the prescribed phase change amount, and the expected characteristics cannot be achieved.